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JAMB Physics 2006 Question 24

Question 24

Alternating Current Circuits

When an a.c. voltage is applied to a capacitor, no power is consumed because the current

  1. A.and voltage are 180° out of phase.
  2. B.and voltage are in phase.
  3. C.lags behind the voltage by 90°.
  4. D.leads the voltage by 90°.
Show the answer and explanation

Answer: D (leads the voltage by 90°.)

Explanation

In a pure capacitor the current leads the voltage by 90°, so the average power (VI cos 90°) is zero: energy stored in one quarter-cycle is returned in the next.